Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
  • H03L7/00—Automatic control of frequency or phase; Synchronisation
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
  • H03L1/00—Stabilisation of generator output against variations of physical values, e.g. power supply
  • H03L1/02—Stabilisation of generator output against variations of physical values, e.g. power supply against variations of temperature only
  • H03L1/022—Stabilisation of generator output against variations of physical values, e.g. power supply against variations of temperature only by indirect stabilisation, i.e. by generating an electrical correction signal which is a function of the temperature

Definitions

• the subject matter of the present application relates to methods and circuits for controlling frequency of an oscillator circuit, in particular, to methods and circuits for reducing frequency variation of crystal oscillators by compensating environmental condition variations such as temperature changes.
• Oscillators are widely used in digital as well as analog integrated circuits for generating critical clocking signals.
• Oscillators may include crystal oscillators, voltage- controlled oscillators, voltage-controlled crystal oscillators and many other types of oscillators. While a crystal oscillator can often provide a relatively constant and accurate output frequency under fixed environmental conditions, the output frequency of a crystal oscillator may nevertheless still vary when environmental conditions vary.
• the present disclosure provides a system for controlling frequency of an oscillator.
• the system includes two or more
• the system also includes a reference signal generation circuit configured to generate a reference signal and a first curve function generation circuit coupled to the two or more temperature sensing circuits and the reference signal generation circuit.
• the first curve function generation circuit is configured to provide two or more curve- generating signals based on the temperature sensing signals and the reference signal.
• the system further includes a summing circuit coupled to the first curve function generation circuit. The summing circuit is configured to provide, based on the two or more curve-generating signals, a first signal for controlling the frequency of the oscillator.
• the present disclosure also provides a method for controlling frequency of an oscillator.
• the method includes generating two or more temperature sensing signals; generating a reference signal; providing two or more curve-generating signals based on the temperature sensing signals and the reference signal; and generating, based on the two or more curve-generating signals, a first signal for controlling the frequency of the oscillator.
• the present disclosure further provides a system for controlling frequency of a voltage controlled oscillator.
• the system includes three or more temperature sensing circuits configured to generate temperature sensing voltages corresponding to temperatures obtained by the three or more temperature sensing circuits.
• the system also includes a reference signal generation circuit configured to generate a reference voltage and a first curve function generation circuit electrically coupled to the three or more temperature sensing circuits and the reference signal generation circuit.
• the first curve function generation circuit is configured to provide three or more curve-generating signals based on the temperature sensing voltages and the reference voltage.
• the three or more curve-generating signals have different signal levels and different curves.
• the first curve function generation circuit is also configured to provide a first signal for controlling the frequency of the oscillator.
• the first signal corresponds to the sum of the three or more curve-generating signals.
• the system further includes a second curve function generation circuit configured to provide a second signal.
• the second signal has a linear relation with respect to temperature variations.
• the system further includes an adder configured to generate, based on the first signal and the second signal, a control voltage for controlling the frequency of the oscillator.
• FIG. 1 is a diagram illustrating exemplary relation of two varying signals and a sum of the two varying signals, with respect to temperature variations.
• FIG. 2A is a block diagram illustrating an exemplary oscillator control circuit.
• FIG. 2B is a diagram illustrating exemplary relation between an output signal of the exemplary oscillator control circuit shown in FIG. 2A and temperature variations.
• FIG. 3A is a schematic diagram of an exemplary embodiment of the oscillator control circuit shown in FIG. 2A.
• FIG. 3B is a schematic diagram of an exemplary summing circuit.
• FIG. 4A is a block diagram illustrating another exemplary oscillator control circuit.
• FIG. 4B is a diagram illustrating exemplary relation between an output signal of the exemplary oscillator control circuit shown in FIG. 4A and temperature variations.
• FIG. 5A is a schematic diagram of an exemplary embodiment of the oscillator control circuit shown in FIG. 4A.
• FIG. 5B is a schematic diagram of another exemplary summing circuit.
• FIG. 5C is a diagram illustrating exemplary current-temperature relation corresponding to the currents shown in FIG. 5A.
• FIG. 6A is a schematic diagram of another exemplary embodiment of the oscillator control circuit shown in FIG. 4A.
• FIG. 6B is a schematic diagram of another exemplary summing circuit.
• FIG. 6C is a diagram illustrating exemplary current-temperature relation corresponding to the currents shown in FIG. 6A.
• FIG. 7A a block diagram illustrating an exemplary temperature-compensated voltage-controlled crystal oscillator (TC-VCXO) circuit.
• FIG. 7B is a diagram illustrating exemplary relation between a control signal of the exemplary TC-VCXO circuit shown in FIG. 7A and temperature variations.
• FIG. 8A is a schematic diagram of an exemplary temperature sensing circuit.
• FIG. 8B is a diagram illustrating exemplary relation between a temperature sensing voltage shown in FIG. 8A and temperature variations.
• FIG. 9 is a flowchart representing an exemplary method for controlling frequency of an oscillator.
• FIG. 1 is a diagram 100 illustrating exemplary relation of two varying signals and a sum of the two varying signals, with respect to the temperature variation.
• the signals and the sum of the signals can be voltage signals or current signals.
• diagram 100 illustrates a first current 11 102, a second current I2 104, and a sum of first current 11 102 and second current I2 104, i.e., a sum current I 106.
• First current 11 102 and second current I2 104 can represent, for example, curve-generating current signals generated in response to temperature sensing signals.
• Temperature sensing signals such as temperature sensing voltages, can be generated in response to variations of temperatures obtained by temperature sensing circuits. The temperature sensing signals and circuits are described in details below.
• first current 11 102 is illustrated as a current curve varying from a low value to a high value.
• Second current I2 104 is illustrated as a current curve varying from a higher value to a lower value.
• the variations of the first current 11 102 and second current I2 104 can be in response to, for example, temperature variations. That is, the horizontal axis of diagram 100 can represent the temperature variations and the vertical axis of diagram 100 can represent the current variations corresponding to the temperature variations.
• first current 11 102 and second current I2 104 can be summed, added, or superimposed to generate sum current I 106.
• first current 11 102 can have a non-linear current curve and second current I2 104 can have a linear current curve.
• a linear curve has a first order component and may not have higher order components.
• a linear current curve can have a constant slope and thus represent a first order relation (e.g., a straight-line type relation) between the current variations and the temperature variations.
• a non-linear curve can have a first order component and higher order (e.g., second and third order) components.
• a non-linear current curve can have more than one slope with respect to temperature variations and thus can represent a higher order relation (e.g., a segmented or curved type relation) between the current variations and the temperature variations.
• first current 11 102 and second current I2 104 are added, summed, or
• sum current I 106 can also have a non-linear curve, which can have higher order (e.g., third order) components.
• First current 11 102 and second current I2 104 can be generated from, for example, a non-linear curve function generation circuit and a linear curve function generation circuit, respectively.
• a non-linear curve function generation circuit can include two or more differential circuits.
• a differential circuit can have two input signals, i.e., a first input signal and a second input signal.
• the first input signal can be a reference voltage signal that has a substantially constant voltage.
• the second input signal can be a varying voltage signal generated from, for example, a temperature sensing circuit in response to the temperature variations. Because the temperature variations sensed by different temperature sensing circuit may be different, various voltage signals can be generated. Therefore, depending on the differences of the voltage levels between the two input signals, the currents flowing through different differential circuits (e.g., current 11 102, and current I2 104) can have various current levels and various current curves.
• the currents having various current levels and various current curves can then be added, summed, or superimposed to generate a non-linear current having higher order (e.g., third order) components (e.g., current I 106).
• a non-linear current having higher order (e.g., third order) components e.g., current I 106.
• Exemplary non-linear curve function generation circuit and linear curve function generation circuit are described in detail below.
• FIG. 2A is a block diagram illustrating an exemplary oscillator control circuit 200.
• Oscillator control circuit 200 can include a first temperature sensing circuit 202, a second temperature sensing circuit 204, a reference signal generation circuit 206, and a curve function generation circuit 208.
• Oscillator control circuit 200 can also include other circuits, such as a voltage or current summing circuit (not shown in FIG. 2A), which can sum, add, or superimpose two or more voltages of currents. It is appreciated that oscillator control circuit 200 can also include any other desired circuit elements.
• first temperature sensing circuit 202 and second temperature sensing circuit 204 can obtain temperature by, for example, sensing or detecting the environmental temperature variations as their input signals. Based on the obtained temperature variations, first temperature sensing circuit 202 and second temperature sensing circuit 204 can generate a temperature sensing signal such as temperature sensing voltages V1 203 and V2 205. Temperature sensing voltages V1 203 and V2 205 can vary in response to the variations of the temperature obtained by first temperature sensing circuit 202 and second temperature sensing circuit 204, respectively. As a result, temperature sensing voltages V1 203 and V2 205 can represent or substantially represent the variations of the temperature. An exemplary temperature sensing circuit is described in detail below corresponding to FIGs. 8A-8B.
• one or more temperature sensing circuits for collecting temperature conditions at different locations on an integrated-circuit chip or a device, one or more temperature sensing circuits, such as first temperature sensing circuit 202 and second temperature sensing circuit 204, can be placed at each location. In some embodiments, one or more temperature sensing circuits can be placed at the same location.
• oscillator control circuit 200 can also include reference signal generation circuit 206, which can generate a reference signal (e.g., a reference voltage signal Vc 207) that is constant or substantially constant with respect to environmental condition variations, such as temperature variations.
• reference signal generation circuit 206 can include a bandgap voltage reference generation circuit capable of providing substantially constant reference voltages across a desired range of temperature variations.
• the reference signal e.g., reference voltage signal Vc 207 can have any value that is desired.
• oscillator control circuit 200 can also include curve function generation circuit 208.
• Curve function generation circuit 208 receives inputs signals (e.g., temperature sensing voltages V1 203 and V2 205, and reference voltage signal Vc 207) from temperature sensing circuits 202 and 204 and reference signal generation circuit 206. After receiving the input signals, curve function generation circuit 208 can compare, for example, the value of each of temperature sensing voltages V1 203 and V2 205 to the value of reference voltage signal Vc 207. As an example, curve function generation circuit 208 can compare both temperature sensing voltages V1 203 and V2 205 with reference voltage signal Vc 207 and generates output signals Voutl 209 and Vout2 210.
• signals e.g., temperature sensing voltages V1 203 and V2 205, and reference voltage signal Vc 207
• curve function generation circuit 208 can also provide two or more curve-generating current signals (e.g., current 11 305A and I2 305B shown in FIG. 3A), which can be added, summed, or superimposed to generate a sum current described below.
• curve function generation circuit 208 can generate output signals as voltage signals (e.g., output signals Voutl 209 and Vout2 210).
• curve function generation circuit 208 can generate output signals as current signals instead of voltage signals.
• Curve function generation circuit 208 can also convert the output voltage signals to output current signals and vice versa. Curve function generation circuit 208 is further described in detail below.
• FIG. 2B is a diagram 240 illustrating exemplary relation between an output signal (e.g., output signal Vout2 210) of the exemplary oscillator control circuit 200 shown in FIG. 2A and temperature variations.
• output signal Vout2 210 is derived from, or corresponds to, the temperature variations obtained by first temperature sensing circuit 202 and second temperature sensing circuit 204.
• output signal Vout2 210 can be used for controlling, such as compensating, the frequency variation of an oscillator (e.g., a voltage controlled oscillator, i.e., VCXO) caused by the temperature variations.
• an oscillator e.g., a voltage controlled oscillator, i.e., VCXO
• the curve of output signal Vout2 210 can have higher order, such as a second and/or third order, components.
• the higher order components can have an impact on the shape of the curve of output signal Vout2 210.
• fine tuning of a control voltage for an oscillator e.g., a VCXO
• a better matching to the oscillator's frequency curve can be provided. Details of using the oscillator control circuit 200 for controlling oscillators are described below corresponding to FIGs. 7A-7B.
• FIG. 3A is a schematic diagram of an exemplary embodiment 300 of oscillator control circuit 200 as shown in FIG. 2A. It is readily appreciated by one of ordinary skill in the art that the illustrated blocks and circuit elements in FIG. 3A can be altered in their numbers or their relative configurations. Exemplary embodiment 300 can also include additional blocks or circuit elements.
• exemplary embodiment 300 can include first and second temperature sensing circuits 202 and 204; reference signal generation circuit 206; and differential circuits 320A and 320B. Differential circuits 320A and 320B can be included in curve function generation circuit 208 shown in FIG. 2A.
• first and second temperature sensing circuits 202 and 204 and reference signal generation circuit 206 can be similar or substantially similar to those described corresponding to FIG. 2A and thus will not be described here.
• differential circuit 320A can include a power supply 301 A, a current source 302A, one or more (e.g., two) resistors R1 304A and R2 306A, and one or more (e.g., two) transistor devices M1 308A and M2 31 OA.
• differential circuit 320B can include a power supply 301 B, a current source 302B, resistors R3 304B and R4 306B, and transistor devices M3 308B and M4 31 OB.
• Transistor devices can be either p-type devices or n-type devices, such as p-type Metal-Oxide- Semiconductor (PMOS) or n-type Metal-Oxide-Semiconductor (NMOS) devices.
• PMOS p-type Metal-Oxide- Semiconductor
• NMOS n-type Metal-Oxide-Semiconductor
• the transistor devices can also have same or different sizes including transistor width and length.
• power supply 301 A can be electrically coupled to current source 302A.
• Power supply 301 A can provide electrical power to differential circuit 320A.
• the voltage of power supply 301 A may vary depending on the applications.
• Current source 302A can provide a constant or substantially constant current.
• current source 302A can include a large-size transistor device controlled by a feedback circuit (not shown) so that the output current of the current source can be maintained substantially constant.
• differential circuit 320A can include a left branch comprising resistor R1 304A and transistor device M1 308A, and a right branch comprising the resistor R2 306A and transistor device M2 31 OA.
• One terminal of resistor R1 304A and one terminal of the resistor R2 306A are electrically coupled to current source 302A.
• the other terminals of resistor R1 304A and resistor R2 306A are electrically coupled to terminals, such as source terminals, of transistor devices M1 308A and M2 31 OA (shown as p-type transistor devices in FIG. 3A), respectively.
• current source 302A is electrically coupled to both the left and the right branches of the differential circuit 320A, a current 1x1 provided by current source 302A is divided between the left and right branches. That is, the sum of the current flowing through the left branch and that of the right branch equals or substantially equals current 1x1 provided by current source 302A.
• transistor device M1 308A includes a gate terminal electrically coupled to first temperature sensing circuit 202.
• the gate terminal of transistor device M1 308A is controlled by temperature sensing voltage V1 203 generated from first temperature sensing circuit 202.
• the gate terminal of transistor device M2 31 OA is electrically coupled to reference signal generation circuit 206.
• the gate terminal of transistor device M2 31 OA receives reference voltage signal Vc 207 generated by reference signal generation circuit 206.
• reference voltage signal Vc 207 can be constant or substantially constant.
• transistor devices M1 308A and M2 31 OA are under different operating conditions because they receive different control voltages at their gate terminals.
• the current flowing through transistor device M1 308A i.e., the left branch
• the current flowing through transistor device M2 31 OA i.e., the right branch
• the current flowing through transistor device M1 308A can be greater than the current flowing through transistor device M2 31 OA.
• transistor devices M1 308A and M2 31 OA are PMOS devices, transistor device M1 308A can have a greater gate-to-source voltage than that of transistor device M2 31 OA.
• transistor devices M1 308A and M2 31 OA are NMOS devices, transistor device M1 308A can have a smaller gate-to-source voltage than that of transistor device M2 31 OA. Accordingly, because the currents flowing through the left and the right branches of differential circuit 320A can be different, the voltage levels of output signal Vouti 209A associated with the left branch and output signal Vout2 21 OA associated with the right branch can also be different.
• differential circuit 320B can include power supply 301 B, current source 302B, resistors R3 304B and R4 306B, and transistor devices M3 308B and M4 31 OB.
• Differential circuit 320B can have a similar or substantially similar configuration as that of differential circuit 320A.
• differential circuit 320B receives temperature sensing voltage V2 205 from second temperature sensing circuit 204 through transistor device M4 310B in its right branch; and receives reference voltage signal Vc 207 generated by reference signal generation circuit 206 through transistor device M3 308B in its left branch.
• the operation of differential circuit 320B can be the same or similar to that of differential circuit 320A, and thus is not described here.
• Differential circuit 320B can generated output signal Vouti 209B and output signal Vout2 210B. Because the currents flowing through the left and the right branches of differential circuit 320B can be different, the voltage levels of output signal Vouti 209B associated with the left branch and output signal Vout2 210B associated with the right branch can also be different.
• FIG. 3B is a schematic diagram of an exemplary summing circuit 340.
• output signals Vouti 209A/B and Vout2 210A/B can be voltage signals.
• output signals Voutl 209A/B and Vout2 210A/B may need to be converted from voltage signals to current signals. Therefore, in some embodiments, one or more instances of summing circuit 340 can be coupled to or integrated with differential circuits 320A and 320B.
• resistors 318A and 318B in summing circuit 340 can be electrically coupled to differential circuit 320A, and similarly differential circuit 320B.
• resistor 318A and 318B can be coupled to output signal Voutl 209A and output signal Vout2 21 OA, respectively, for converting output signal Voutl 209A and output signal Vout2 21 OA from voltage signals to current signals.
• one terminal of resistor 318A and one terminal of resistor 318B can be electrically coupled to electrical ground.
• the other terminals of resistor 318A and resistor 318B can be electrically coupled to output signal Voutl 209A and output signal Vout2 21 OA, respectively.
• one or more instances of summing circuit 340 can also be electrically coupled to differential circuit 320B.
• summing circuit 340 can also be any other summing circuit that is desired.
• summing circuit 340 can also add, sum, or superimpose current signals.
• one or more instances of summing circuit 340, through terminals of resistor 318B, can be coupled to output signal Vout2 21 OA and output signal Vout2 210B.
• the current flowing through both right branches of differential circuits 320A and 320B i.e., current 11 305A and current I2 305B
• a sum current e.g., sum current I 317 flowing through resistor 318B.
• current 11 305A and current I2 305B can have different values and curves.
• the sizes of the transistor devices and the resistors in differential circuits 320A and 320B can be different such that same temperature sensing voltages V1 203 and V2 205 may generate different currents 11 305A and I2 305B.
• differential circuits 320A and 320B receive different temperature sensing voltages V1 203 and V2 205 and therefore generates different currents 11 305A and I2 305B.
• Currents 11 305A and I2 305B can also be linear or non-linear.
• Currents 11 305A and I2 305B can be each at a different level so that a coarse and/or a fine tuning of sum current I 317 can be realized.
• current 11 305A can be at a high level so that it represents the coarse tuning. That is, adjusting current 11 305A can cause a relatively large change of sum current I 317.
• current I2 305B can be at a low level so that it represents the fine tuning. That is, adjusting current I2 305B can cause a relatively small change of sum current I 317.
• sum current I 317 is derived from, or corresponds to, the temperature variations obtained by first temperature sensing circuit 202 and second temperature sensing circuit 204, sum current I 317 can be used for controlling or compensating the frequency change of the oscillator due to the temperature variations.
• the curve of sum current I 317 can have higher order, such as a third order, components. The higher order components can have an impact on the shape of the curve of sum current I 317. Therefore, by adjusting the shape of the curve of sum current I 317, a better matching to the oscillator's frequency curve can be provided.
• FIG. 4A is a block diagram illustrating another exemplary oscillator control circuit 400.
• Oscillator control circuit 400 can include a first temperature sensing circuit 402, a second temperature sensing circuit 404, a third temperature sensing circuit 406, a reference signal generation circuit 408, and a curve function generation circuit 410.
• Oscillator control circuit 400 can also include other circuits, such as a summing circuit (not shown in FIG. 4A), which can generate the sum of the voltages of currents. It is appreciated that oscillator control circuit 400 can also include any other desired circuit elements.
• First temperature sensing circuit 402, second temperature sensing circuit 404, third temperature sensing circuit 406, and reference signal generation circuit 408 can be the same as or similar to the temperature sensing circuits and reference signal generation circuit shown in FIG. 2A and thus will not be described here. Based on the corresponding temperature variations, first temperature sensing circuit 402, second temperature sensing circuit 404, and third temperature sensing circuit 406 can generate output signals such as temperature sensing voltages V1 403, V2 405, and V3 407. Temperature sensing voltages V1 403, V2 405, and V3 407 can vary in response to the variations of the temperature obtained by first temperature sensing circuit 402, second temperature sensing circuit 404, and third temperature sensing circuit 406, respectively.
• Curve function generation circuit 410 can receive input signals (e.g., temperature sensing voltages V1 403, V2 405, and V3 407, and reference voltage signal Vc 409) from first temperature sensing circuit 402, second temperature sensing circuit 404, third temperature sensing circuit 406, and reference signal generation circuit 408. After receiving the input signals, curve function generation circuit 410 can compare, for example, the value of each of temperature sensing voltages V1 403, V2 405, and V3 407 to the value of reference voltage signal Vc 409. As an example, curve function generation circuit 410 compares all temperature sensing voltages V1 403, V2 405, and V3 407 with reference voltage signal Vc 409 and generates output signal Voutl 412 and Vout2 414.
• input signals e.g., temperature sensing voltages V1 403, V2 405, and V3 407, and reference voltage signal Vc 409
• Vc 409 reference voltage signal
• curve function generation circuit 410 can also generate one or more (e.g., three) current signals (current signals 11 505A, I2 505B, and I3 505C) shown in FIG. 5A), which are added, summed, or superimposed together to generate a sum current described below.
• curve function generation circuit 410 generates output signals as voltage signals (e.g., output signals Voutl 412 and Vout2 414).
• curve function generation circuit 410 can generate output signals as current signals instead of voltage signals. Curve function generation circuit 410 can also convert the output voltage signals to output current signals and vice versa. Curve function generation circuit 410 is further described in detail below.
• FIG. 4B is a diagram 440 illustrating exemplary relation between an output signal (e.g., output signal Vout2 414) of the exemplary oscillator control circuit 400 shown in FIG. 4A and temperature variations.
• output signal Vout2 414 is derived from, or corresponds to, the temperature variations obtained by first temperature sensing circuit 402, second temperature sensing circuit 404, and third temperature sensing circuit 406.
• output signal Vout2 414 can be used for controlling, such as compensating, the frequency variation of an oscillator (e.g., a VCXO) caused by the temperature variations.
• the curve of output signal Vout2 414 can have higher order, such as a second and/or third order, components.
• the higher order components can have an impact on the shape of the curve of output signal Vout2 414.
• fine tuning of a control voltage for an oscillator e.g., a VCXO
• a better matching to the oscillator's frequency curve can be provided.
• FIG. 5A is a schematic diagram of an exemplary embodiment 500 of oscillator control circuit 400 as shown in FIG. 4A. It is readily appreciated by one of ordinary skill in the art that the illustrated blocks and circuit elements in FIG. 5A can be altered in their numbers or their relative configurations. Exemplary embodiment 500 can also include additional blocks or circuit elements.
• exemplary embodiment 500 can include first, second, and third temperature sensing circuits 402, 404, and 406, reference signal generation circuit 408, and differential circuits 520A, 520B, and 520C. Differential circuits 520A, 520B, and 520C can be included in curve function generation circuit 410 shown in FIG. 4A.
• first, second, and third temperature sensing circuits 402, 404, and 406 and reference signal generation circuit 408 can be similar or substantially similar to those described corresponding to FIG. 2A and thus will not be described here.
• differential circuits 520A/B/C can include power supplies 501 A/B/C, current sources 502A/B/C, one or more resistors R1 504A, R2 506A, R3 504B, R4 506B, R5 504C, and R6 506C, and one or more transistor devices M1 508A, M2 51 OA, M3 508B, M4 51 OB, M5 508C, and M6 510C.
• the transistor devices e.g., M1 508A and M2 51 OA
• the transistor devices can be either p-type devices or n-type devices, such as PMOS or NMOS devices.
• the transistor devices can also have same or different sizes including transistor width and length.
• resistors R1 504A, R2 506A, R3 504B, R4 506B, R5 504C, and R6 506C, and transistor devices M1 508A, M2 51 OA, M3 508B, M4 510B, M5 508C, and M6 510C, can be substantially the same as or similar to those of differential circuits 320A/B described above, and thus will not be described.
• the parameters of the circuit elements in FIG. 5A such as the sizes of the transistor devices, may or may not be the same as those corresponding elements shown in FIG. 3A.
• transistor devices M1 508A and M3 508B can include gate terminals that are electrically coupled to first temperature sensing circuit 402 and second temperature sensing circuit 404, respectively.
• the gate terminals of transistor device M1 508A and M3 508B are controlled by temperature sensing voltages V1 403 and V2 405 generated from first temperature sensing circuit 402 and second temperature sensing circuit 404, respectively.
• the gate terminals of transistor devices M2 51 OA and M4 51 OB are electrically coupled to reference signal generation circuit 408. Therefore, the gate terminals of transistor device M2 51 OA and M4 510B receive reference voltage signal Vc 409 generated by the reference signal generation circuit 408. As described above, reference voltage signal Vc 409 can be constant or substantially constant.
• differential circuit 520C receives temperature sensing voltage V3 407 from temperature sensing circuit 406 through the gate terminal of transistor device M6 510C in the right branch of differential circuit 520C.
• Differential circuit 520C also receives reference voltage signal Vc 409 provided by the reference signal generation circuit 408 through the gate terminal of transistor device M5 508C in the left branch of differential circuit 520C.
• Vc 409 provided by the reference signal generation circuit 408 through the gate terminal of transistor device M5 508C in the left branch of differential circuit 520C.
• the circuit configuration of differential circuits 520A/B/C can also be any other type such that it enables comparison of temperature sensing voltages V1 403, V2 405, and V3 407, and reference voltage signal Vc 409.
• transistor devices M1 508A and M2 51 OA are under different operating conditions because they receive different control voltages at their gate terminals. As a result, the current flowing through transistor device M1 508A and the current flowing through transistor device M2 51 OA can be different. As an example, if temperature sensing voltage V1 403 has a value that is less than that of reference voltage signal Vc 409, the current flowing through transistor device M1 508A can be greater than the current flowing through transistor device M2 51 OA.
• transistor devices M1 508A and M2 51 OA are PMOS devices, transistor device M1 508A can have a greater gate-to-source voltage than that of transistor device M2 51 OA.
• transistor devices M1 508A and M2 51 OA are NMOS devices, transistor device M1 508A can have a smaller gate-to-source voltage than that of transistor device M2 51 OA. Accordingly, because the currents flowing through the left and the right branches of differential circuit 520A can be different, the voltage levels of output signal Voutl 512A associated with the left branch and output signal Vout2 514A associated with the right branch can also be different.
• differential circuit 520B can have a similar or substantially similar configuration as that of differential circuit 520A.
• differential circuit 520B receives temperature sensing voltage V2 405 from second temperature sensing circuit 404 through transistor device M3 508B in its left branch; and receives reference voltage signal Vc 409 generated by reference signal generation circuit 408 through transistor device M4 510B in its right branch.
• the operation of differential circuit 520B can be the same or similar to that of differential circuit 520A, and thus is not described here.
• Differential circuit 520B can generate output signal Voutl 512B and output signal Vout2 514B. Because the currents flowing through the left and the right branches of differential circuit 520B can also be different, the voltage levels of output signal Voutl 512B associated with the left branch and output signal Vout2 514B associated with the right branch can also be different.
• Differential circuit 520C can have a similar or substantially similar
• differential circuit 520C receives temperature sensing voltage V3 407 from third temperature sensing circuit 406 through transistor device M6 510C in its right branch; and receives reference voltage signal Vc 409 generated by reference signal generation circuit 408 through transistor device M5 508C in its right branch.
• the operation of differential circuit 520C can be the same or similar to that of differential circuit 520A/B, and thus is not described here.
• Differential circuit 520C can generated output signal Voutl 512C and output signal Vout2 514C. Because the currents flowing through the left and the right branches of differential circuit 520C can be different, the voltage levels of output signal Voutl 512C associated with the left branch and output signal Vout2 514C associated with the right branch can also be different.
• FIG. 5B is a schematic diagram of another exemplary summing circuit 540.
• output signals Voutl 512A/B/C and Vout2 514A/B/C can be voltage signals.
• output signals Voutl 512A/B/C and Vout2 514A/B/C may need to be converted from voltage signals to current signals. Therefore, in some embodiments, one or more instances of summing circuit 540 can be coupled to or integrated with differential circuits 520A/B/C.
• differential circuit 520A, and similarly differential circuits 520B and 520C can to coupled to resistors 518A and 518B of summing circuit 540.
• resistors 518A and 518B can be coupled to output signal Voutl 512A and output signal Vout2 514A, respectively, for converting voltage signals to current signals.
• one terminal of resistor 518A and one terminal of resistor 518B can be electrically coupled to electrical ground.
• the other terminals of resistor 5 8A and resistor 518B can be electrically coupled to output signal Voutl 512A and output signal Vout2 514A, respectively.
• one or more instances of summing circuit 540 can also be coupled to differential circuits 520B and 520C.
• summing circuit 540 can also be any other summing circuit that is desired.
• summing circuit 540 can also add, sum, or superimpose current signals.
• one or more instances of summing circuit 540, through terminals of resistor 518B, can be coupled to output signals Vout2 514A, Vout2 514B, and Vout2 514C.
• the current flowing through right branches of differential circuits 520A, 520B, and 520C can be summed, added, or superimposed to generate a sum current (e.g., sum current I 517 flowing through resistor 518B).
• Currents 11 505A, I2 505B, and I3 505C can be the same or different.
• the sizes of the transistor devices and the resistors in differential circuits 520A, 520B, and 520C can be different such that same input voltages may generate different currents 11 505A, I2 505B, and I3 505C.
• differential circuits 520A, 520B, and 520C receive different temperature sensing voltages V1 403, V2 407, and V3 407 and therefore generates different currents 11 505A, I2 505B, and I3 505C.
• FIG. 5C is a diagram 560 illustrating exemplary current-temperature relation corresponding to currents 11 505A, I2 505B, and I3 505C.
• currents 11 505A, I2 505B, and I3 505C can be linear or non-linear.
• Currents 11 505A, I2 505B, and I3 505C can be at different levels so that coarse and/or fine tuning of sum current I 517 can be provided.
• current 11 505A may be at a highest level so that it represents the coarsest tuning. That is, adjusting current 11 505A can cause a relatively large change of sum current I 517.
• current I3 505C can be at a lowest level so that it represents the finest tuning. That is, adjusting current I3 505C can cause a smallest change of sum current I 517.
• Current I2 505B can be at a middle level between currents 11 505A and I3 505C. Thus, adjusting current I2 505B can cause a medium change of sum current I 517.
• sum current I 517 is derived from, or corresponds to, the temperature variations sensed by first, second, and third temperature sensing circuits 402, 404, and 406, sum current I 517 can be used for controlling or compensating the frequency change of the oscillator due to the temperature variations.
• first, second, and third temperature sensing circuits 402, 404, and 406 can generate different currents 11 505A, I2 505B, and I3 505C in response to same or different temperature variations.
• the curves of currents 11 505A, I2 505B, and I3 505C can have higher order, such as third order, components.
• sum current I 517 can also have higher order, such as a third order, components.
• the higher order components can have an impact on the shape of the curve of sum current I 517.
• currents 11 505A, I2 505B, and I3 505C correspond to three temperature sensing circuits shown in FIG.
• an additional degree of freedom for adjusting sum current I 517 can be provided as compared to the degree of freedom for adjusting sum current I 317 as shown in FIG. 3A, where two temperature sensing circuits are used.
• an additional degree of freedom for adjusting the current level and the current curve of sum current I 517 an improved fine tuning of a control voltage for an oscillator (e.g., a VCXO) and a better matching to the oscillator's frequency curve can be provided.
• FIG. 6A is a schematic diagram of another exemplary embodiment 600 of oscillator control circuit 400 as shown in FIG. 4A. It is readily appreciated by one of ordinary skill in the art that the illustrated blocks and circuit elements in FIG. 6A can be altered in their numbers or their relative configurations. Exemplary embodiment 600 can also include additional blocks or circuit elements.
• exemplary embodiment 600 can include first, second, and third temperature sensing circuits 402, 404, and 406; reference signal generation circuit 408; and one or more (e.g., four) differential circuits 620A, 620B, 620C, and 620D.
• Differential circuits 620A, 620B, 620C, and 620D can be included in curve function generation circuit 410 shown in FIG. 4A.
• first, second, and third temperature sensing circuits 402, 404, and 406 and reference signal generation circuit 408 can be similar or substantially similar to those described corresponding to FIG. 2A and thus will not be described here.
• differential circuits 620A/B/C/D can include similar circuit elements as those shown in differential circuits 520A/B/C in FIG. 5A.
• differential circuits 620A/B/C/D can include, among other things, one or more transistor devices M1 608A, M2 61 OA, M3 608B, M4 610B, M5 608C, M6 610C, M7 608D, and M8 610D. It is readily appreciated by one of ordinary skill in the art that the number of circuit elements, such as resistors and transistors, can be any number not limited to that shown in FIG. 6A.
• the transistor devices can be either p-type devices or n-type devices, such as PMOS or NMOS devices.
• the transistor devices can also have same or different sizes including transistor width and length.
• the circuit configurations of differential circuits 620A/B/C/D can be substantially the same as or similar to those of differential circuits 520A/B/C described above, and thus will not be described here.
• the parameters of the circuit elements in FIG. 6A such as the sizes of the transistor devices, may or may not be the same as those corresponding elements shown in FIG. 5A.
• transistor devices M1 608A and M3 608B can include gate terminals that are electrically coupled to first temperature sensing circuit 402 and second temperature sensing circuit 404, respectively.
• the gate terminals of transistor device M1 608A and M3 608B are controlled by the temperature sensing voltages V1 403 and V2 405 generated from first temperature sensing circuit 402 and second temperature sensing circuit 404, respectively.
• the gate terminals of transistor devices M2 61 OA and M4 610B are electrically coupled to reference signal generation circuit 408. Therefore, the gate terminals of transistor device M2 61 OA and M4 610B receive reference voltage signal Vc 409 generated by the reference signal generation circuit 408. As described above, reference voltage signal Vc 409 can be constant or substantially constant.
• differential circuits 620C and 620D receive
• Differential circuits 620C and 620D also receive reference voltage signal Vc 409 generated by reference signal generation circuit 408 through the gate terminal of transistor device M6 610C in the right branch of differential circuit 620C and the gate terminal of transistor device M7 608D in the left branch of differential circuit 620D.
• differential circuits 620A/B/C/D can also be any other type such that it enables comparison of temperature sensing voltages V1 403, V2 405, and V3 407, and reference voltage signal Vc 409.
• Differential circuits 620A and 620B can operate, such as compare
• differential circuits 620C and 620D can also operate, such as compare temperature sensing voltage V3 407 with reference voltage signal Vc 409 in a substantially the same or similar manner as that described above corresponding to differential circuits 520A and 520B.
• differential circuits 620A/B/C/D can generated output signal Voutl 612A/B/C/D and output signal Vout2 614A/B/C/D.
• FIG. 6B is a schematic diagram of another exemplary summing circuit 640.
• output signals Voutl 612A/B/C/D and Vout2 614A/B/C/D can be voltage signals.
• output signals Voutl 612A/B/C/D and Vout2 614A/B/C/D may need to be converted from voltage signals to current signals. Therefore, in some embodiments, one or more instances of summing circuit 640 can be coupled to or integrated with differential circuits 620A/B/C/D.
• differential circuit 620A, and similarly differential circuit 620B, 620C, and 620D can be coupled to resistors 618A and 618B.
• resistors 618A and 618B can be coupled to output signal Voutl 612A and output signal Vout2 614A, respectively, for converting voltage signals to current signals.
• one terminal of resistor 618A and one terminal of resistor 618B can be electrically coupled to electrical ground.
• the other terminals of resistor 618A and resistor 618B can be electrically coupled to output signal Voutl 612A and output signal Vout2 614A, respectively.
• one or more instances of summing circuit 640 can also be coupled to differential circuits 620B, 620C, and 620D. As a result, by using one or more instances of summing circuit 640, output voltage signals Voutl 612A/B/C/D and Vout2 614A/B/C/D can be converted to current signals. It is
• summing circuit 640 can also be any other summing circuit that is desired.
• summing circuit 640 can also add, sum, or superimpose current signals.
• one or more instances of summing circuit 640, through terminals of one or more instances of resistor 618B, can be coupled to output signals Vout2 614A, Vout2 614B, Vout2 614C, and Vout2 614D.
• the current flowing through right branches of differential circuits 620A, 620B, 620C, and 620D can be summed, added, or superimposed to generate a sum current (e.g., sum current I 617 flowing through resistor 618B).
• currents 11 605A, I2 605B, I3 605C, and I4 605D can be the same or different.
• the sizes of the transistor devices and the resistors in differential circuits 620A, 620B, 620C, and 620D can be different such that same input voltages may generate different currents 11 605A, I2 605B, I3 605C, and I4 605D.
• differential circuits 620A, 620B, 620C, and 620D can receive different temperature sensing voltages V1 403, V2 405, and V3 407, and may generate different currents 11 605A, I2 605B, I3 605C, and I4 605D.
• FIG. 6C is a diagram 660 illustrating exemplary current-temperature relation corresponding to currents 11 605A, I2 605B, I3 605C, and I4 605D. As shown in FIG. 6C, currents 11 605A, I2 605B, I3 605C, and I4 605D can be linear or non-linear.
• Currents 11 605A, I2 605B, I3 605C, and I4 605D can be at different levels so that coarse and/or fine tuning of sum current I 617 can be provided.
• current 11 605A may be at a highest level so that it represents the coarsest tuning. That is, adjusting current 11 605A can cause a largest change of sum current I 617.
• current I4 605D can be at a lowest level so that it represents the finest tuning. That is, adjusting current I4 605D can cause a smallest change of sum current I 617.
• Currents I2 605B and I3 605C can be at middle levels between currents 11 605A and I4 605C.
• sum current I 617 is derived from, or corresponds to, the temperature variations sensed by first, second, and third temperature sensing circuits 402, 404, and 406, sum current I 617 can be used for controlling or compensating the frequency change of the oscillator due to the temperature variations.
• first, second, and third temperature sensing circuits 402, 404, and 406 can generate different currents 11 605A, I2 605B, I3 605C, and I4 605D corresponding to same or different temperature variations.
• the curves of currents 11 605A, I2 605B, I3 605C, and I4 605D can have higher order, such as third order, components.
• sum current I 617 can also have higher order, such as a third order, components.
• the higher order components can have an impact on the shape of the curve of sum current I 617.
• currents 11 605A, I2 605B, I3 605C, and I4 605D correspond to four temperature sensing circuits shown in FIG. 6A, one additional degree of freedom for adjusting the level and the curve of sum current I 617 is provided as compared to the degree of freedom provided by embodiment 500 of oscillator control circuit 400 shown in FIG. 5A, where three temperature sensing circuits are used.
• FIG. 7A is a block diagram illustrating an exemplary temperature- compensated voltage-controlled crystal oscillator (TC-VCXO) circuit 700.
• TC-VCXO temperature- compensated voltage-controlled crystal oscillator
• TC-VCXO circuit 700 can include a first curve function generation circuit 702, a second curve function generation circuit 704, an adder 710 and a voltage-controlled crystal oscillator (VCXO) 714.
• first curve function generation circuit 702 can be any of the curve function generation circuits (e.g., curve function generation circuits 208 and 410) and their various embodiments described above in FIGs. 2A, 3A, 4A, 5A, and 6A.
• first curve generation circuit 702 can generate a voltage or current signal (e.g., signal S1 ), which represents the temperature variations obtained by the temperature sensing circuits (e.g., first, second, and third temperature sensing circuits 402, 404, and 406 in FIG. 6A).
• the curve of signal S1 can have higher order (such as third order) components.
• First curve function generation circuit 702 can also be any variations or modifications of the curve function generation circuits and their various embodiments described above in FIGs. 2A, 3A, 4A, 5A, and 6A.
• second curve function generation circuit 704 can be any type of circuit that can generate a linear voltage or current signal (e.g., signal S2) with respect to the temperature variations.
• Signal S2 can be a signal that is, for example, in linear relation with its input signal within a partial or a whole input signal range.
• the input signal to second curve function generation circuit 704 can be a temperature sensing signal generated from a temperature sensing circuit.
• the output signal of second curve function generation circuit 704 can be a voltage or current signal that varies with a constant slope in response to the input temperature sensing signal.
• second curve function generation circuit 704 can be an inverting amplifier receiving input signals from one or more temperature sensing circuits.
• adder 710 can be any type of circuits, digital or analog, that performs addition, summation, or superimposition of the input signals of adder 710.
• adder 710 can be a mixer, a summing operational amplifier, a translinear or a Gilbert-type circuit, etc.
• Adder 710 can add, sum, or superimpose one or more input signals that are voltage signals or current signals (e.g., signals S1 and S2) and generate a corresponding output voltage or current signal (e.g., VCTC 712).
• the curve of VCTC 712 can have, for example, a desired curve and voltage level such that VCTC 712 can be provided as a control voltage for controlling frequency of an oscillator (e.g., VCXO 714).
• VCTC 712 can be provided as a control voltage for controlling frequency of an oscillator (e.g., VCXO 714).
• FIG. 7B is a diagram 740 illustrating exemplary relation between VCTC 712 shown in FIG. 7A and the temperature variations.
• VCTC712 can have any curve that is desired to provide control and matching of the oscillator's frequency curve.
• VCXO 714 can be, for example, a crystal oscillator with voltage controlled capacitors. Supplied with a control voltage (e.g., VCTC 712), VCXO 714 can partially or substantially adjust, such as tune, the dependence on temperature of the resonant frequency of the crystal oscillator of VCXO 714. That is, VCTC 712 can be supplied to VXCO 714 in order to control or compensate the frequency change of the crystal oscillator of VCXO 714.
• VCTC 712 can be supplied to VXCO 714 in order to control or compensate the frequency change of the crystal oscillator of VCXO 714.
• a frequency variation of the crystal oscillator caused by a temperature variation can be compensated by applying a proper control voltage VCTC 712, which is then multiplied by the crystal oscillator's gain such that the frequency of the crystal oscillator can be increased or decreased to a desired value.
• FIG. 8A illustrates an exemplary temperature sensing circuit 800.
• Temperature sensing circuit 800 can also include additional blocks or circuit elements. Temperature sensing circuit 800 can be included in, for example, temperature sensing circuits 202 and 204 in FIGs. 2A and 3A; and temperature sensing circuits 402, 404, and 406 in FIGs. 4A, 5A, and 6A.
• temperature sensing circuit 800 can include a power supply 801 , a first transistor device 802, a resistor 804, a second transistor device 806, and an electrical ground 808.
• Power supply 801 can provide electrical power to temperature sensing circuit 800.
• First transistor device 802 can be a PMOS device electrically coupled to power supply 801 through its source terminal.
• First transistor device 802 can also be an NMOS device electrically coupled to power supply 801 through its drain terminal.
• the gate terminal of first transistor device 802 can be controlled by a biasing voltage such that first transistor device 802 can provide a desired current flowing through resistor 804 and second transistor device 806.
• first transistor device 802 is a PMOS or NMOS device
• the drain or source terminal of first transistor device 802 is electrically coupled to a terminal of resistor 804.
• Resistor 804 can generate a voltage drop from a first terminal electrically coupled to first transistor device 802 to a second terminal electrically coupled to second transistor device 806.
• Resistor 804 can also limit the current flowing through temperature sensing circuit 800.
• the second terminal of resistor 804 is electrically coupled to a first terminal (e.g., a collector terminal) of second transistor device 806.
• Second transistor device 806, as shown in FIG. 8A can be a PNP-type bipolar transistor.
• the second and third (e.g., the base and emitter) terminals of second transistor device 806 can be electrically coupled together, such that second transistor device 806 can function as a forward-biased PN junction diode device, which can be used as a temperature sensor.
• Second transistor device 806 e.g., a forward-biased PN junction diode device
• Second transistor device 806 can exhibit a linear relationship between the forward-bias voltage and the temperature.
• Second transistor device 806 can have a negative temperature coefficient.
• the second transistor device 806 can also be an NPN-type bipolar transistor, a diode, or any other type of device that may exhibit a linear voltage-temperature relationship.
• temperature sensing circuit 800 can generate a temperature sensing voltage V 803 that has a linear relationship with temperature variations.
• FIG. 8B is a diagram 840 illustrating exemplary relation between a temperature sensing signal, such as temperature sensing voltage V 803, shown in FIG. 8A and the temperature variations.
• temperature sensing voltage V 803 can be measured at the third (e.g. drain) terminal of first transistor device 802.
• diagram 840 illustrates that temperature sensing voltage V 803 can vary linearly or substantially linearly with the temperature variations. Accordingly, temperature sensing circuit 800 can be used to measure the temperature variations in a linear manner.
• FIG. 9 is a flowchart representing an exemplary method for controlling frequency of an oscillator. It will be readily appreciated that the illustrated procedure can be altered to delete steps or further include additional steps.
• a system e.g., system 200
• two or more temperature sensing circuits e.g., temperature sensing circuits 202 and 204
• Temperature sensing voltages can vary in response to the variations of the temperature obtained by the two or more temperature sensing circuits.
• temperature sensing voltages can represent or substantially represent the variation of the temperature.
• temperature sensing signals can be generated by using a temperature sensor (e.g., a forward-biased PN junction diode device) that exhibits a linear relationship between the forward-bias voltage and the temperature.
• a temperature sensor e.g., a forward-biased PN junction diode device
• the system via a reference signal generation circuit (e.g., reference signal generation circuit 206), generates (930) a reference signal that is constant or substantially constant with respect to environmental condition variations, such as temperature variations.
• a reference signal can be generated by a reference signal generation circuit (e.g., a bandgap voltage reference generation circuit) that is capable of providing substantially constant reference voltages across a desired range of temperature variations.
• the reference signal can have any value that is desired.
• the system After generating the temperature sensing signals and the reference signal, the system, via a curve function generation circuit (e.g., curve function generation circuit 208), provides (940) two or more curve-generating signals, such as currents, based on the temperature sensing signals and the reference signal.
• a curve function generation circuit e.g., curve function generation circuit 208
• the two or more curve-generating currents can be provided by comparing the reference signal and the corresponding temperature sensing signal.
• the two or more curve-generating currents can also have different current levels and different curves for providing coarse and fine tuning of the sum of the curve-generating currents and for providing better matching to the oscillator frequency curve.
• the system After providing the two or more curve-generating signals, the system, via a summing circuit (e.g., summing circuit 340) generates (950), based on the two or more curve-generating signals, a first signal (e.g., sum current I 317) for controlling the frequency of the oscillator.
• a first signal e.g., sum current I 317
• the first signal can have a curve that includes one or more third or higher order components. And the curve of the first signal corresponds to the current levels and the curves of the two or more curve-generating currents.
• method 900 can proceed to a stop 960.
• Method 900 can also proceed to further steps (not shown), including providing a second signal (e.g., signal S2 708), which can have a linear relation with respect to temperature variations; and generating, based on the first current and the second current, a control voltage for controlling the frequency of the oscillator. It is appreciated by one of ordinary skill in the art that method 900 can also be repeated as desired.
• a second signal e.g., signal S2 708
• a control voltage for controlling the frequency of the oscillator.

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